The present invention relates, in general, to electronics, and more particularly, to methods of forming semiconductor devices and structure.
In the past, various configurations were used to form power supply controllers that controlled an output voltage on a secondary side of transformer by controlling current flow through a primary side of the transformer. In some cases, and optical coupler was utilized to sense the value of the output voltage and form a feedback signal that was used to control the current through the primary side. However, this added cost to the system. In other cases, the transformer included an auxiliary winding into which a voltage was induced from the primary side of the transformer. The signals on the auxiliary winding were used to control a power supply controller connected to the primary side of the transformer. One such control circuit is disclosed in U.S. Pat. No. 7,102,899 issued to Reinhard et al on Sep. 5, 2006. One problem with these prior circuits was the accuracy of the regulation of the output voltage when using the auxiliary winding as a control signal. Typically, the accuracy was less than approximately ten percent. Another problem was limiting the value of the current in the secondary winding to a maximum value. Without connecting directly to the secondary winding, it was difficult to limit the value of the secondary current.
Accordingly, it is desirable to have a control method that reduces the system cost, that does not utilize an optical coupler to form a feedback signal, that has improved accuracy, and that limits the value of the secondary current.
For simplicity and clarity of the illustration, elements in the figures are not necessarily to scale, and the same reference numbers in different figures denote the same elements. Additionally, descriptions and details of well-known steps and elements are omitted for simplicity of the description. As used herein current carrying electrode means an element of a device that carries current through the device such as a source or a drain of an MOS transistor or an emitter or a collector of a bipolar transistor or a cathode or anode of a diode, and a control electrode means an element of the device that controls current through the device such as a gate of an MOS transistor or a base of a bipolar transistor. Although the devices are explained herein as certain N-channel or P-Channel devices, a person of ordinary skill in the art will appreciate that complementary devices are also possible in accordance with the present invention. It will be appreciated by those skilled in the art that the words during, while, and when as used herein are not exact terms that mean an action takes place instantly upon an initiating action but that there may be some small but reasonable delay, such as a propagation delay, between the reaction that is initiated by the initial action. The use of the word substantially means that a value of element has a parameter that is expected to be very close to a stated value or position. However, as is well known in the art there are always minor variances that prevent the values or positions from being exactly as stated. It is well established in the art that variances of up to about ten percent (10%) are regarded as reasonable variances from the ideal goal of exactly as described.